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1、Versatile Pathway to Functional Telechelics via RAFT Polymerization and Click ChemistrySudershan R. Gondi, Andrew P. Vogt, and Brent S. Sumerlin*Department of Chemistry, Southern Methodist UniVersity, 3215 Daniel AVenue, Dallas, Texas 75275-0314ReceiVed August 24, 2006; ReVised Manuscript ReceiVed N
2、oVember 14, 2006ABSTRACT: Two novel azidofunctionalized chain transfer agents (CTAs) were prepared and subsequently employed to mediate the reversible addition-fragmentation chain transfer (RAFT) polymerizations of styrene (Sty) and N,N-dimethylacrylamide (DMA) under a variety of conditions. Trithio
3、carbonate 2-dodecylsulfanylth- iocarbonylsulfanyl-2-methyl-propionic acid 3-azido-propyl ester and dithioester 4-cyano-4-methyl-4-thiobenzoyl- sulfanyl-butyric acid 3-azido-propyl ester successfully mediated the polymerizations of Sty and DMA. Both RAFT polymerizations exhibited pseudo-first-order k
4、inetics and a linear Mndependence with conversion. The resulting homopolymers (Mn) 4 - 22 103g/mol and Mw/Mne 1.33) were demonstrated to have retained end group functionality, as evidenced by the successful formation of block copolymers. The R-azido terminal polymers and the azidofunctionalized CTAs
5、 were coupled with high efficiency by click chemistry to various alkynes (propargyl acrylate, propargyl methacrylate, and propargyl alcohol) in the presence of a Cu(I) catalyst, demonstrating the ability to prepare a range of functional telechelics and CTAs.IntroductionControlled/living radical poly
6、merization (CRP) techniques facilitate the preparation of (co)polymers with predetermined molecular weights, narrow molecular weight distributions, and high degrees of chain end functionalization.1While resulting in control comparable to living ionic polymerizations, CRP methods can be conducted und
7、er less stringent conditions and offer the additional advantage of enhanced functional group tolerance.2-10Despite the versatility of CRP techniques, post- polymerization modification is a viable means to incorporate functionality potentially incompatible with polymerization, characterization, or pr
8、ocessing conditions.11,12In particular, functionalization of end groups retained during CRP is a potential method to prepare, for example, fluorescently labeled chains,13,14bioconjugates,15,16and surface-immobilized poly- mers.17,18However, because of the inherent low concentration of end groups and
9、 the possibility of side reactions with other functional groups within the polymer, reactions with high efficiency and fidelity are necessary for successful and specific polymer modification. With the use of a Cu(I) catalyst, azide-alkyne coupling reactions result in highly specific and efficient pr
10、eparation of 1,4-disubstituted 1,2,3-triazole products under moderate reaction conditions.19,20This particular coupling process can be con- ducted in aqueous or organic media, and little or no side reactions are observed. The practicality and versatility of the Cu(I)-catalyzed coupling reaction led
11、to its inclusion in the class of efficient and specific organic reactions, commonly termed “click chemistry”, as coined by Sharpless et al.21 Combining the synthetic techniques of CRP and click chemistry provides an efficient route to functional polymeric materials. Several groups reported the synth
12、esis of (co)polymers via CRP and subsequent azide-alkyne coupling reactions, although the significant majority of these reports concern the modification of (co)polymers prepared by atom transfer radicalpolymerization(ATRP)ornitroxide-mediatedpolymerization.14,22-37 For example, Lutz et al. demonstra
13、ted the preparation of -functional telechelics from polymers prepared by ATRP via end group substitution with NaN3and subsequent coupling with various functional alkynes.31We reported the preparation of -(meth)acryloyl macromonomers via ATRP and azide-alkyne coupling.38While this approach proved an
14、efficient and specific means to prepare macromonomers with a high degree of end group functionalization from any monomer polymerizable by ATRP, we seek to expand the method to other radically polymerizable monomer classes. Reversible addition-fragmentation chain transfer (RAFT) polymerization and ma
15、cromolecular design via exchange of xanthates have emerged as some of the most promising CRP methods due to facile experimental setup and applicability to a wide range of monomers.7-10It is advantageous to extend the pairing of CRP and click chemistry to capitalize on the flexibility of RAFT polymer
16、ization and the efficiency and specificity of click chemistry to prepare functionalized materials. Previously, OReilly et al. reported the RAFT block copolymerization of a protected acetylene-containing monomer. After deprotection, the resulting block polymers were subsequently employed to prepare shell-crosslinked micelles with cores susceptible to functional- ization with low-molecular-weight azides.39The same authors also reported alkynyl-functionalized RAFT agents being em- ployed to
